It is desirable in today's marketplace to produce a dry table wine with a low-alcohol concentration (4% to 10% by weight) to meet the demands of a health conscious public. Ideally, these wines should not sacrifice full body, aroma and character when compared to traditional table wines. Such low-alcohol wines are sometimes referred to as "light wines."
Traditional table wine is made by crushing grapes to produce a mass, referred to by those skilled in the art as must, which includes grape skins, seeds (assuming a seeded variety), water, invert sugar and a number of organic compounds which contribute to the character and quality of the final product, such as the aroma, bouquet and flavor of the wine. To make red wine the entire must is fermented. This is necessary because the color pigments which give the wine its red color are primarily found in the grape skins. Alternatively, the red must can be heated with the addition of an extraction agent such as, for example, SO.sub.2 to extract the color pigments. The must is then separated into a juice fraction colored red from the pigments extracted from the skins and a solids fraction, commonly referred to as pomace, containing the skins, seeds and trace amounts of sugar and water. After separation, most of the organic compounds mentioned above are in the grape juice fraction and are intact. The juice fraction is then fermented to produce a red wine.
In the case of blush wines and particularly in the case of white wines, the color pigments found in the grape skins must be removed early in the wine-making process to control coloring of the wine. Accordingly, prior to fermentation, the must is separated into a grape juice fraction and pomace. The separation is carried out in a settling tank, and that portion of the grape juice which cannot be removed by gravity separation is obtained by pressing or squeezing the skins and seeds in a wine press. After separation, most of the organic compounds referred to above are in the grape juice fraction and are intact.
Once the juice has been separated, it is ready to be fermented. Fermentation is usually carried out in a batch fermentation vessel, and the temperature is controlled to produce an isothermal fermentation. The temperature set-point is usually set between 55 and 65 degrees Fahrenheit. If, for example, it is assumed that the maturity of the grapes was such that the juice contained 19% invert sugar by weight prior to fermentation, and the fermentation was carried out to dryness (0% sugar), the resultant wine would contain 9.71% alcohol by weight based on a stoichiometric balance using the Gay-Lussac equation. In "The Technology of Wine Making", Third Edition. by Amerine, Berg, and Cruess, researchers report actual alcohol yields of 90 to 95 percent of theoretical yields. Assuming this to be true, Table I shows the expected and theoretical alcohol concentrations for various grape maturities. All data in Table I is shown in percent by weight (by volume).
TABLE I Theoretical Actual Alcohol Sugar Alcohol Yield 16.00 8.17 (10.08) 7.35-7.76 (9.09-9.58) 17.00 8.68 (10.70) 7.81-8.24 (9.64-10.16) 18.00 9.20 (11.32) 8.28-8.74 (10.21-10.77) 19.00 9.71 (11.93) 8.73-9.22 (10.76-11.35) 20.00 10.22 (12.54) 9.19-9.71 (11.31-11.93) 21.00 10.73 (13.15) 9.66-10.20 (11.87-12.52) 22.00 11.24 (13.76) 10.10-10.68 (12.40-13.09)
The microbiological processes that occur during fermentation produce trace amounts of organic compounds which further add to the character and quality of the wine. This so where the must is directly fermented to produce red wine and in the case where the grape juice is first separated from the must and then fermented to produce a red, white or blush wine. A more complete discussion of the chemistry of fermentation and the composition of wines can be found in "Technology of Wine Making", by Amerine, Berg, and Cruess, Third Edition, pages 177 to 244. Once the traditional wine is fermented, it is fined, filtered, processed, and bottled for the consumer.
Existing methods of making low-alcohol wines fall into two categories. The first method involves picking grapes with a very low-sugar content and fermenting the juice as described above. This method does not produce a good quality product, because the grape has not fully matured. The second method is to take traditional wines and fractionate them into a low-alcohol portion, and a high-alcohol portion. This second method is discussed below.
Wine may be thought of in simplistic terms as a water-alcohol mixture which can be separated into a high-alcohol fraction and a low-alcohol fraction. The low-alcohol fraction becomes the low-alcohol wine. Many different processes can be used to do the fractionation including, vacuum distillation, pressure distillation, thin filmed evaporation under reduced pressured, or reverse osmosis. Most commercially made low-alcohol wines are made in this fashion.
The problem with this method of manufacture is that all of the fractionation processes available today partially remove, destroy, or separate into the wrong fraction the organic compounds whose presence determines to a large extent the character and quality of the product. As discussed above these compounds are generated in the fermentation or are present in the original must or grape juice. Experienced wine tasters will often describe the resultant product as containing a "processed character" or "cooked" taste when compared to traditional wine made from the same must or grape juice. The low-alcohol wine will lack fruitiness, bouquet, aroma, and character. It is low in quality.